This invention relates, in general, to facilitating request processing within a logically partitioned computing system, and more particularly, to facilitating quiesce request processing within a logically partitioned computer system.
The processing of a request by one processor may affect one or more other processors of a computer system. For example, in a Symmetric Multi-Processor (SMP) system based on the z/Architecture® of International Business Machines Corporation, Armonk, N.Y., various broadcast purge operations, such as Invalidate Page Table Entry (IPTE), Invalidate DAT Table Entry (IDTE), Set Storage Key Extended (SSKE), and Compare and Swap and Purge (CSP) instructions, require entries of one or more buffers (e.g., Translation Lookaside Buffers (TLBs)) to be removed from the buffers in all processors of the computing environment. Furthermore, the architecture requires the buffers to be purged atomically, such that no processor can observe a new TLB entry, while some other processor observes an old entry. Many other computer architectures also provide a similar mechanism.
One common implementation for a broadcast purge operation includes the following: 1) processors are quiesced (i.e., most normal processing operations are suspended, including accessing the TLB); 2) TLBs on the processors are purged of the appropriate entries; 3) the common resource is changed (e.g., a page table entry in storage for IPTE or a storage key for SSKE); and 4) finally, the quiesce is released and the processors continue normal processing activities. Obviously, this implementation might have a performance impact, especially for large SMP configurations, since essentially all processors of the system are to be quiesced for the duration of the operation. In particular, it is common that one processor may be executing a long running instruction that is not interruptible, so that it cannot reach the quiesce state for a period of time, and other processors are required to wait for this one processor to reach the quiesce state before the steps described above can be completed.